We have observed the excitability of rat neural progenitor cells (NPCs) and characterized the profile of the voltage-gated ion channels, with the help of the electrophysiological measurements in NPCs in vitro, in order to clarify the electrophysiological property of NPCs. The membrane potential changes of neural progenitors were detected with fluorescent dye bis-(1,3-dibutylbarbituric acid) trimethine oxonol (DiBAC4(3)) by a confocal laser scanning microscope. The changes of fluorescent intensity of DiBAC4(3) stain after KCl stimulation were slight which indicated that the NPCs were inexcitable. Under the current-clamp, spontaneous discharge was not detected and the action potential was failed to be elicited. These findings were consistent with the result from DiBAC4(3) staining. Under the voltage clamp, the NPCs expressed two types of outward K(+) currents with no evidence for Na(+) currents. An outward delayed rectifier type K(+) current and outward transient K(+) current were elicited. Our findings demonstrate NPCs' electrophysiological properties: the electrical inexcitability indicated by the presence of two types of K(+) currents and the absence of Na(+) current.